A conventional steam-cooling-type gas turbine has been disclosed in, for example, Japanese Patent Application Laid-Open No. 11-182205 filed by the applicant of the present invention. The steam-cooling-type gas turbine described in this reference will be explained with reference FIG. 12 and FIG. 13.
In FIG. 12, reference numeral 100 indicates a blade ring. The blade ring 100 is provided with one-half ring-shape members that are longitudinally combined so as to be detachably attached to each other, thereby forming a ring shape. In the blade ring 100, plurality of (for example, 32) front-stage stator blades (for example, first-stage stator blades) 101 and a rear-stage blade (for example, 2nd-stage stator blade) 102 are arranged in a ring shape. A 3rd-stage stator blade, a 4th-stage stator blade, a 5th-stage stator blade, and so no are arranged in a ring shape in the steam-cooling-type gas turbine.
The blade ring 100 has an integral structure in which the portion on which the front-state blades 101 are arranged and the portion on which the rear-stage stator blade 102 are arranged are integrally formed into one part. In the steam-cooling-type gas turbine, in addition to the blade ring integral structure, there is another structure, that is, a blade ring separated structure in which the blade ring having the front-stage blades arranged thereon and the blade ring having the rear-stage blades arranged thereon are provided as separated members, with the blade ring on the front-stage stator blade side and the blade ring on the rear-stage stator blade side being connected by another member.
The blade ring 100 is provided with a steam supplying passage 103, a steam communication passage 104 and a steam recovering passage 105 respectively. At least one set of the steam supplying passage 103, the steam communication passage 104 and the steam recovering passage 105 is provided in the one-half ring-shaped blade ring 100. Further, cooling steam passages 106 and 107 are respectively formed in each of the front-stage stator blades 101 and the rear-stage stator blades 102.
A first branch pipe 108, a second branch pipe 109, a third branch pipe 110 and a fourth branch pipe 111 are respectively placed between the steam supplying passage 103 and the cooling steam passage 106 of the front-stage stator blades 101, between the steam communication passage 104 and the cooling steam passage 106 of the front-stage stator blades 101, between the steam communication passage 104 and the cooling steam passage 107 of the rear-stage stator blades 102, and between the steam recovering passage 105 and the cooling steam passage 107 of the rear-stage stator blades 102.
The blade ring 100 is supported by a not shown casing. A not shown rotor side is attached to the casing so as to be freely rotate thereon, and a moving blade (for example, first-stage moving blade) 112 is placed in a ring shape.
The moving blade 112 is placed on the downstream side of the stator blades 101, 102. The moving blade 112 is placed between-the front-stage stator blade 101 and the rear-stage stator blade 102. Moreover, the chip of the moving blade 112 on the rotary side is allowed to face the blade ring 100 on the fixed side with a clearance 113 in between. It is essential to maintain the clearance 113 evenly so as to improve the efficiency of the gas turbine.
When the steam-cooling-type gas turbine is driven, a high-temperature, high-pressure combustion gas (not shown) is allowed to pass through the front-stage blades 101, the moving blade 112 and the rear-stage stator blade 102 so that the moving blade 112 and the rotor side are rotated to generate a torque.
Cooling steam, indicated by a solid-line arrow in FIG. 12, is supplied to the steam supplying passage 103. Then, the cooling steam is distributed from the steam supplying passage 103 to the respective cooling steam passages 106 of the front-stage stator blades 101 through the first branch pipe 108. The cooling steam thus distributed is allowed to cool the front-stage stator blades 101 through the respective steam passage 106.
The cooling steam that has cooled the front-stage stator blades 101 is concentrated into the steam communication passage 104 through the second branch pipe 109, and again distributed to the respective cooling steam passage 107 of the rear-stage stator blades 102 from the steam communication path 104 through the third branch pipe 110. The cooling steam, thus distributed, is allowed to cool the rear-stage stator blades 102 through the respective cooling steam passages 107.
The cooling steam that has cooled the rear-stage stator blades 102 is again concentrated on the steam recovering passage 105 through the fourth branch pipe 111, and recovered from the steam recovering passage 105. The steam thus recovered is recycled.
The conventional steam-cooling-type gas turbine is arranged so as to communicate the cooling steam passage 106 on the front-state stator blades 101 (for example, 8 to 16) side and the cooling steam passage 107 on the rear-state stator blades 102 (for example, 8 to 16) with each other collectively through a single steam communication passage 104.
For this reason, as illustrated in FIG. 13, the number of the steam communication passage 14 is fewer and arranged in the blade ring 100 in a scattered manner. Consequently, of the blade ring 100, the portion having the steam communication passage 104 has a higher temperature, while the portion without this passage has a lower temperature, with a great temperature gap. The thermal deformation of the blade ring 100 becomes greater due to the irregularity of temperature distribution having a great temperature gap, resulting in an uneven clearance 113 between the blade ring 100 on the fixed side and the moving blade 112 on the rotary side.
Besides the steam-cooling-type gas turbine of the blade ring integrated structure, the problem is commonly seen in the steam-cooling-type gas turbine of the blade ring separated structure.